The capacity and speed of communications systems may be increased by transmitting information in optical form over networks composed of optically transmissive nodes, fibers, waveguides, and the like. High capacity optical communications systems require that many optical signals be frequency division multiplexed in the components of an optical network. This requires that there be a way of conveniently detecting a single electromagnetic frequency and separating it from a plurality of multiplexed electromagnetic frequencies. An ideal device for detecting a single optical frequency and separating it from a plurality of multiplexed frequencies is a frequency selective optical filter. Until now, there has been no convenient approach to creating a suitable optical filter tunable to a large number of optical frequencies. The performance of prior filters has been limited in terms of tuning speed, frequency selectivity, or tuning range. All of these prior devices also have been expensive to implement.